The instant invention relates to dispensers for viscous fluids and more particularly to a dispenser-gun assembly which is operative for effectively and accurately dispensing controlled amounts of a viscous fluid and to a dispenser for the dispenser-gun assembly.
The general concept of selectively dispensing a viscous fluid from a pressurizable chamber through a reduced dispensing nozzle has been known for many years and has been effectively embodied in a wide variety of dispensing apparatus for dispensing various types of viscous fluids and pastes. In this regard, various dispenser-gun assemblies have heretofore been widely used for dispensing various viscous fluids and pastes, including various lubricants, sealants, and caulking materials. Dispenser-gun assemblies of this type have generally comprised dispenser units including elongated tubular members, piston elements which are snugly yet slidably received in the tubular members thereof and nozzles which communicate with the interiors of the tubular members thereof for dispensing fluids therefrom as the piston elements thereof are advanced in the tubular members. Dispenser-gun assemblies of this type have generally further comprised double pawl type ratcheting dispenser guns which are operative for advancing the pistons of dispensers in the respective tubular members thereof for dispensing fluids from the tubular chamber. The dispenser guns of dispenser-gun assemblies of this type have generally included squeezable handle and trigger assemblies which are operative for advancing the pistons of dispensers in the respective tubular members thereof and for maintaining the pistons in advanced positions when the trigger portions of the dispenser guns are released. As a result, the heretofore available dispenser-gun assemblies have generally been operative by squeezing the trigger portions of the dispenser guns thereof for advancing the pistons of the dispensers received therein in stepped increments. However, they have generally not been operative for automatically releasing the pressures applied to fluids contained in the dispensers thereof after dispensing operations have been completed.
Various more sophisticated dispensers and dispenser-gun assemblies have also been heretofore available for more precisely dispensing controlled amounts of viscous fluids, such as various epoxies, solder pastes and solder creams. The heretofore available dispensers for dispensing fluids of these types have generally been more similar in construction to conventional medical syringes and they have comprised barrel portions having tubular cylindrical chambers therein, nozzle portions including reduced dispensing tips or needles and piston elements which are slidably received in sealing engagement in the barrel portions thereof so that they are advanceable toward the respective nozzle portions thereof for dispensing fluids from the chambers thereof. Dispensers of this type have generally comprised elastomeric piston elements which are received in the barrel portions thereof with relatively high levels of interference fit to seal between the barrel portions and piston elements thereof. Dispensers of this type have generally been utilized in combination with gun assemblies which are similar in concept and operation to the double pawl ratchet type gun assemblies hereinabove described but which are adapted to effect somewhat more precise movement of the pistons of syringe type dispensers in the chamber thereof. Alternatively, dispensers of this type have been utilized in combination with pneumatic dispensing apparatus which have been operative for applying controlled amounts of air pressure to the pistons of dispensers in order to advance the pistons thereof in their respective chambers.
One of the main disadvantages of the heretofore available dispensing apparatus of the above described types is that they have generally been operative with significant amounts of post extrusion which occurs after the desired amounts of fluids have been dispensed from the cylinders or barrel portions thereof. Post extrusion is generally caused by the expansion of the pressurized fluids remaining in dispensers after the desired amounts of fluids have been dispensed therefrom. In this regard, while most pure viscous fluids are essentially non compressible, it has been found that many viscous fluids contain substantial quantities of entrapped air which cause them to exhibit significant levels of compressibility. It has been further found that because the heretofore available dispensers have generally had relatively high levels of frictional resistance between the pistons and the barrel portions thereof, the pistons of the heretofore available dispensers have not been sufficiently freely movable to relieve the pressures on fluids contained therein, even after all of the externally applied forces have been removed from the pistons thereof. Consequently, virtually all of the heretofore available dispensers of this general type have been found to operate with excessive amounts of post extrusion and it has not been possible to dispense accurate quantities of viscous fluids from the previously known piston-cylinder type fluid dispensers.
The instant invention provides an effective dispenser-gun assembly and dispenser which are operative for dispensing viscous fluids without significant amounts of post extrusion. In this regard, the dispenser of the instant invention is adapted to minimize the frictional resistance between the piston and cylinder thereof so that the piston is freely moveable in a reverse direction in the cylinder thereof to relieve pressure on a fluid contained in the cylinder while nevertheless maintaining an effective seal between the piston and the cylinder wall. The dispenser gun which is operative in combination with the dispenser includes a drive plunger which is operative for advancing the piston in the cylinder. However, while the dispenser gun is adapted so that it is manually actuatable for advancing the drive plunger to advance the piston in the cylinder, it is further adapted so that the drive plunger is automatically retracted to release the pressure applied to the piston by the plunger unless the dispenser gun is operated to manually maintain the piston in an advanced position. Accordingly, unless the actuating mechanism of the dispenser gun is manually held in an actuated position at the end of a dispensing operation, the drive plunger is automatically retracted so that it is disengaged or partially disengaged from the piston. Further, because the dispenser is constructed to minimize the frictional resistance between the piston and the cylinder, the piston is freely movable in a rearward or reverse direction in the cylinder to relieve the expansive forces in a fluid contained in the cylinder.
The dispenser of the instant invention which is adapted to minimize post extrusion comprises an elongated tubular barrel member having an elongated cylindrical chamber therein, the chamber having a zero draft throughout its effective length, a nozzle element on one end of the barrel member and a piston element which is slidably received in the chamber so that it is operative for applying pressure to a fluid contained in the chamber. The piston element and the barrel member are preferably constructed so that the frictional resistance between the piston element and the barrel member is between approximately 0.5 and 2.5 pounds per square inch of barrel cross sectional area. The piston element is preferably received in the chamber with an interference fit of between 0.02 inches and 0.07 inches and it is preferably made of a thermoplastic material having a flexual modulus of between 180,000 pounds per square inch and 210,000 pounds per square inch. Further, because the barrel member has a zero draft throughout its length, the interference fit between the piston element and the barrel member is substantially uniform throughout the length of the barrel member. The piston element preferably includes a circular front end wall portion and a tubular skirt portion which extends rearwardly from the front end wall portion. The skirt portion preferably includes an annular front wiping lip adjacent the front end wall portion, an annular rear wiping lip which is spaced rearwardly from the front wiping lip and a recessed intermediate portion of preferably concave configuration which extends between the front and rear wiping lips. The front wiping lip preferably tapers forwardly and outwardly to a forward wiping edge, and it is preferably partially defined by an undercut annular notch which extends rearwardly and inwardly from the forward wiping edge. The front wiping lip is preferably received in the chamber with an interference fit of between 0.002 inches and 0.007 inches and the front and rear wiping lips are preferably spaced by an amount equal to approximately one half of the diameter of the chamber. The piston element is preferably made of low density polyethylene and the barrel member is preferably made of a thermoplastic material other than polyethylene.
The dispenser gun of the instant invention comprises a drive plunger which is receivable in engagement with the piston element of a dispenser of the above type and mechanical advancing means for mechanically advancing the drive plunger in order to mechanically advance the piston element in the chamber thereof. The mechanical advancing means is adapted so that it is operative for mechanically advancing the drive plunger from a first position in the chamber to a second or inwardly advanced position therein and for immediately, automatically, mechanically returning the drive plunger to the first position in the chamber unless the advancing means manually maintained in a position wherein the drive plunger is in an advanced or partially advanced position in the chamber. The dispenser gun preferably includes a handle section and the advancing means preferably includes a trigger section which is manually resiliently squeezable or compressible toward the handle section for advancing the drive plunger element from a first position in the chamber to a second further advanced position therein. Further, the advancing means is constructed so that the drive plunger element is automatically and immediately returned to the first position thereof and so that the trigger section is automatically resiliently returned to the initial or unsqueezed position thereof unless the trigger section is manually held in an actuated, squeezed or partially squeezed position. The drive plunger preferably includes a plunger rod having a plurality of sequential notches therein and the advancing means preferably includes a pawl member attached to the trigger section which is engageable with the rod in one of the notches for advancing the drive plunger element from the first position thereof to the second position thereof in the chamber as the trigger section is squeezed toward the handle section and for returning the drive plunger element to the first position thereof when the trigger section is released.
It has been found that the dispenser and the dispenser-gun assembly of the instant invention can be effectively utilized for accurately and precisely dispensing a viscous fluid without significant amounts of post extrusion. In this regard, because of the construction of the piston element and of the resiliency and low friction characteristics of the material from which it is preferably constructed and because of the zero draft construction of the barrel member and the low friction characteristics of the material from which the barrel member is preferably constructed, the piston element is capable of effecting an essentially leak proof seal between the piston element and the barrel member while nevertheless being relatively freely slidable in the barrel member. Further, because the dispenser gun is constructed so that the plunger element is automatically retracted unless it is manually maintained in an advanced or partially advanced position in the chamber, the plunger element is automatically retracted from the piston element at the end of a dispensing operation. Consequently, the piston element can freely move rearwardly in the barrel member at the end of a dispensing operation to relieve the pressure on the fluid remaining in the barrel member and to thereby eliminate any significant post extrusion from the dispenser.
Accordingly, it is a primary object of the instant invention to provide an effective dispenser which is operative for dispensing a viscous fluid without significant amounts of post extrusion.
Another object of the instant invention is to provide a dispenser comprising a piston element and a barrel member wherein the piston element is slidable in a reverse direction in the barrel member with minimal frictional resistance.
Another object of the instant invention is to provide a dispenser-gun assembly which is operative for dispensing a viscous fluid without significant amounts of post extrusion.
An even still further object of the instant invention is to provide a dispenser-gun assembly comprising a dispenser gun including a plunger element which is manually advanceable for dispensing a fluid from a dispenser but which is automatically retracted unless manually maintained in an advanced position.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.